The present invention relates to a stimulable phosphor sheet employable in a radiation image recording and reproducing method utilizing stimulated emission from a stimulable phosphor.
As a method replacing a conventional radiography using a combination of a radiographic film and radiographic intensifying screens, a radiation image recording and reproducing method utilizing a stimulable phosphor was proposed and is practically employed. The method employs a radiation image storage panel comprising a stimulable phosphor layer (i.e., stimulable phosphor sheet) provided on a support, and the procedure of the method comprises the steps of causing the stimulable phosphor of the sheet to absorb radiation energy having passed through an object or having radiated from an object; sequentially exciting the stimulable phosphor with an electromagnetic wave such as visible light or infrared rays (hereinafter referred to as xe2x80x9cstimulating raysxe2x80x9d) to release the radiation energy stored in the phosphor as light emission (i.e., stimulated emission); photoelectrically detecting the emitted light to obtain electric signals; and reproducing the radiation image of the object as a visible image from the electric signals. The panel thus processed is subjected to a step for erasing a radiation image remaining therein, and then stored for the next recording and reproducing procedure. Thus, the radiation image storage panel can be repeatedly employed.
In general, a support and a protective film are provided on the top and bottom surfaces of the stimulable phosphor sheet (or layer), respectively. The stimulable phosphor sheet (or layer) generally comprises a binder and stimulable phosphor particles dispersed therein, but it may consist of agglomerated phosphor without binder. The phosphor sheet containing no binder can be formed by deposition process or firing process. Further, the sheet comprising agglomerated phosphor soaked with a polymer is also known. For the aforementioned method, any types of the stimulable phosphor sheets are employable.
The radiation image recorded in the stimulable phosphor sheet is generally read by the steps of applying stimulating rays onto the front surface side (the phosphor layer side) of the phosphor sheet, collecting light emitted by the phosphor particles by means of a light-collecting means from the same side, and photoelectrically converting the light into image signals. A system for reading the image from one side of the panel in this manner is referred to as xe2x80x9csingle-side reading systemxe2x80x9d. However, there is a case that the light emitted by the phosphor particles should be collected-from both sides (i.e., the front and the back surface sides) of the phosphor sheet. For instance, there is a case that the emitted light is desired to be collected as much as possible. There also is a case that the radiation image recorded in the phosphor layer varies along the depth of the layer, and that it is desired to detect the variation. A system for reading the image from both sides of the phosphor sheet is referred to as xe2x80x9cdouble-side reading systemxe2x80x9d.
The radiation image recording and reproducing method is often used in radiography for medical diagnosis. In that case, it is especially desired to obtain a radiation image of high quality (particularly, high sharpness for high resolution) by applying a small dose of radiation. Therefore, the stimulable phosphor sheet is required to have a high sensitivity and to provide an image of high quality.
The sharpness of radiation image is mainly affected by diffusion or scattering of the stimulating rays in the phosphor sheet or layer. The procedure for reading the latent image comprises the steps of sequentially scanning a beam of the stimulating rays on the surface of the phosphor sheet to induce the stimulated emission, and successively collecting and detecting the emission. If the stimulating rays diffuse or scatter (horizontally in particular) in the sheet, it excites the phosphor not only at the target spot but also in the periphery. Consequently, the stimulated emission emitted from the target position is collected together with that from the periphery. Such contamination of the emissions impairs the sharpness of the resultant image.
For avoiding the diffusion or scattering of the stimulating rays, it has been proposed to divide the plane of the stimulable phosphor sheet into small sections (cells) with a partition reflecting the stimulating ray.
Japanese Patent Provisional Publication No. 59-202100 discloses a stimulable phosphor sheet having a honey-comb structure consisting of many small cells filled with a stimulable phosphor. The panel comprises a substrate and a stimulable phosphor layer provided thereon, and the honey-comb structure, sectioned with a partition is further provided on the phosphor layer.
Japanese Patent Provisional Publication No. 62-36599 discloses a stimulable phosphor sheet employing a support provided with many hollows regularly arranged on one surface. The hollows are filled with a stimulable phosphor, and the ratio of depth to diameter of each hollow is 3.5 or more.
Japanese Patent Provisional Publication No. 5-512636 discloses a process for preparing pixel phosphors with a mold.
Japanese Patent Provisional Publication No. 2-129600 discloses a storage panel employing a support plate having many holes vertically bored and filled with a stimulable phosphor.
Further, Japanese Patent Provisional Publication No. 2-280100 discloses a stimulable phosphor sheet employing a substrate having a honey-comb micro-structure filled with a stimulable phosphor.
In each aforementioned known panel employing a support or substrate provided with many holes or hollows incorporated with a phosphor, a part of the support or substrate serves as a partition preventing the simulating rays from diffusion. That panel, therefore, is useful for improving quality (particularly, sharpness) of the resultant image. On the other hand, since the partition of support material partly occupies the phosphor layer, the amount of the phosphor incorporated in a unit volume of the layer is often too small to absorb enough amount of radiation. Consequently, the partition lowers the sensitivity of the stimulable phosphor sheet. Although the sensitivity can be enhanced by thickening the phosphor layer, a thick phosphor layer generally impairs the sharpness.
In radiography for medical diagnosis, a stimulable phosphor sheet of high sensitivity can reduce a dose of radiation to be applied to a patient. Therefore, it is needed to provide a stimulable phosphor sheet giving an image of higher sharpness with higher sensitivity.
The invention resides in a stimulable phosphor sheet for a radiation image recording and reproducing method comprising the steps of recording a radiation image as a latent image, irradiating the latent image with stimulating rays to release stimulated emission, and electrically processing the emission to reproduce the radiation image, comprising a stimulable phosphor-containing grid partition that two-dimensionally divides the phosphor sheet on its plane to give plural small rectangular sections, and stimulable phosphor-incorporated areas which are rectangularly sectioned with the grid partition and which have a reflectance at the wavelength of the stimulating rays which differs from that of the grid partition.
The above-mentioned stimulable phosphor sheet of the invention is preferably produced by a process which comprises the steps of:
(i) producing plural stimulable phosphor films A and plural stimulable phosphor films B having a reflectance at the wavelength of the stimulating rays which differs from that of the films A;
(ii) forming a multi-layered composition block in which the stimulable phosphor films A and the stimulable phosphor films B are alternately piled up under the condition that neighboring phosphor films A and B would be placed in close contact with each other;
(iii) repeatedly slicing the multi-layered composition block in the direction perpendicular to the plane of the piled films, to prepare plural striped phosphor films in which strips of the stimulable phosphor films A and B are alternately arranged;
(iv) forming another multi-layered composition block in which the striped phosphor films and the stimulable phosphor films B are alternately piled up under the condition that neighboring striped film and stimulable phosphor film B would be placed in close contact with each other; and,
(v) slicing repeatedly the multi-layered composition block formed in the step (iv) in the direction perpendicular to the plane of the piled films, so as to give a stimulable phosphor sheet which comprises a stimulable phosphor-containing grid partition two-dimensionally dividing the phosphor sheet on its plane to give plural small rectangular sections, and stimulable phosphor-incorporated areas which are rectangularly sectioned with the grid partition and which have a reflectance at the wavelength of the stimulating rays which differs from that of the grid partition.
The invention also resides in a stimulable phosphor sheet for a radiation image recording and reproducing method comprising the steps of recording a radiation image as a latent image, irradiating the latent image with stimulating rays to release stimulated emission, and electrically processing the emission to reproduce the radiation image, comprising a grid partition that contains a phosphor absorbing the radiation and emitting light in a UV or visible wavelength region and two-dimensionally divides the phosphor sheet on its plane to give plural small rectangular sections, and stimulable phosphor-incorporated areas which are rectangularly sectioned with the grid partition and which have a reflection property differing from that of the grid partition at the wavelength of the stimulating rays.
The above-mentioned stimulable phosphor sheet of the invention is preferably produced by a process comprising the steps of:
(i) producing plural stimulable phosphor films A and plural phosphor films B which contain a phosphor absorbing the radiation and emitting light in a UV or visible wavelength region and which have a reflectance differing from that of the films A at the wavelength of the stimulating rays;
(ii) forming a multi-layered composition block in which the stimulable phosphor films A and the phosphor films B are alternately piled up under the condition that neighboring phosphor films A and B would be placed in close contact with each other;
(iii) repeatedly slicing the multi-layered composition block in the direction perpendicular to the plane of the piled films, to prepare plural striped phosphor films in which strips of the phosphor films A and B are alternately arranged;
(iv) forming another multi-layered composition block in which the striped phosphor films and the phosphor films B are alternately piled up under the condition that neighboring striped film and phosphor film B would be placed in close contact with each other; and
(v) slicing repeatedly the multi-layered composition block formed in the step (iv) in the direction perpendicular to the plane of the piled films, so as to give a stimulable phosphor sheet which comprises a UV or visible light-emitting phosphor-containing grid partition two-dimensionally dividing the phosphor sheet on its plane to give plural small rectangular sections, and stimulable phosphor-incorporated areas which are rectangularly sectioned with the grid partition and which have a reflectance at the wavelength of the stimulating rays which differs from that of the grid partition.
The invention further resides in a process for producing a stimulable phosphor sheet, comprising the steps of:
(i) producing plural stimulable phosphor films A and plural reflective material films B;
(ii) forming a multi-layered composition block in which the stimulable phosphor films A and the reflective material films B are alternately piled up under the condition that neighboring films A and B would be placed in close contact with each other;
(iii) repeatedly slicing the multi-layered composition block in the direction perpendicular to the plane of the piled films, to prepare plural striped phosphor films in which strips of the films A and B are alternately arranged;
(iv) forming another multi-layered composition block in which the striped phosphor films and the reflective material films B are alternately piled up under the condition that neighboring striped film and film B would be placed in close contact with each other; and
(v) slicing repeatedly the multi-layered composition block formed in the step (iv) in the direction perpendicular to the plane of the piled films, so as to give a stimulable phosphor sheet which comprises a reflective material-containing grid partition two-dimensionally dividing the phosphor sheet on its plane to give plural small rectangular sections, and stimulable phosphor-incorporated areas which are rectangularly sectioned with the grid partition.
In the stimulable phosphor sheet of the invention, the stimulable phosphor-incorporated areas preferably contain at least stimulable phosphor particles and a binder. The stimulable phosphor-containing grid partition preferably contains stimulable phosphor particles and a binder. The phosphor-containing grid partition may preferably contain a binder and phosphor particles absorbing the radiation and emitting light in a UV or visible wavelength region. Otherwise, the grid partition may preferably contain light-reflecting particles and a binder.
The phosphor sheet of the invention preferably has a layer of reflecting the stimulating rays or stimulated emission, which is provided on the surface opposite to the surface on which the stimulating rays are applied. The top and the bottom of the partition may exposed on the surface of the phosphor sheet, or both or one of them may be buried under the phosphor sheet. Preferably, the height of the partition is in the range of 1/3 to 1/1 of the thickness of the phosphor sheet.
Since the stimulable phosphor sheet of the invention gives an image of high sharpness with high sensitivity in the radiation image recording and reproducing method, it is very appropriate to employ the stimulable phosphor sheet of the invention for radiographic medical diagnosis. Further, that stimulable phosphor sheet can be easily, precisely and efficiently produced by the process of the invention.